The present invention relates generally to sensor and guide wire assemblies, in which one or many sensors is/are mounted preferably at the distal end of a guide wire for intravascular measurements of physiological variables in a living body, and in particular in relation to the communication with the sensor(s).
Sensor and guide wire assemblies in which a sensor is mounted at the distal end of a guide wire are known. In U.S. Pat. No. Re. 35,648, which is assigned to the present assignee, an example of such a sensor and guide wire assembly is disclosed, where a sensor guide comprises a sensor element, an electronic unit, a signal transmitting cable connecting the sensor element to the electronic unit, a flexible tube having the cable and the sensor element disposed therein, a solid metal wire (also called a core wire), and a coil attached to the distal end of the solid wire. The sensor element comprises a pressure sensitive device, e.g. a membrane, with piezoresistive elements connected in a Wheatstone bridge-type of arrangement mounted thereon. An exemplifying electrical circuit arrangement can also be found in the present applicant's U.S. Pat. No. 6,343,514. As an alternative, the pressure sensitive device can also be in the form of a resonant structure, as is disclosed in the present applicant's U.S. Pat. Nos. 6,182,513 and 6,461,301. Instead of using cables to connect a sensor element to an electronic unit, other ways of receiving sensor signals can be employed. U.S. Pat. Nos. 6,615,067 and 6,692,446, which are assigned to the present assignee, disclose sensor systems for signal transmission via body tissues and passive biotelemetry, respectively.
Many different types of sensors are illustrated in the cited prior art, and many are based upon the piezoresistive effect where the changing of electrical resistance of a material is due to applied mechanical stress. The piezoresistive effect differs from the piezoelectric effect. In contrast to the piezoelectric effect, the piezoresistive effect only causes a change in resistance, it does not produce electrical charges. Piezoresistors are resistors made from a piezoresistive material and are usually used for measurement of mechanical stress. They are the simplest form of piezoresistive devices.
Thus, the above sensors are passive sensors where a physiological variable is sensed and transmitted directly as a resistance, a current, a voltage, etc. being representative of physiological variable.
Normally, the sensor is powered by a separate micro cable and the sensor signal is transmitted from the sensor to the proximal end of the guide wire via two other micro cables for further processing by a connected processing unit.
Signal transmission from such sensors may be hampered by cable/connector effects, e.g. cable resistance temperature coefficients, contact resistance, leakage due to wetting etc. and bending and mechanical strain on the wire causes disturbances.
If multiple sensors are to be used each sensor requires a separate set of micro cables, and if multiple cable strands and connector elements are used they may severely limit the mechanical performance of a guide wire, and in addition they are difficult to manufacture and are thus prone to reliability issues.
The object of the present invention is to achieve an guide wire assembly that obviates the above drawbacks related to guide wires provided with numerous micro cables, in particular in multi sensor arrangements.